Electrochemical system with concentration recirculation in cyclic batch mode

Abstract

A method of operating an electrochemical device includes periodically discharging a volume of concentrate reject in a timed batch cycle and replacing the concentrate reject with feed water. An electrochemical water treatment system includes a recycle line having a valve controlled by a control module. The control module periodically opens the valve to discharge concentrate reject from the recycle line in a batch timed cycle. The recycle line is fed with feed water to replace the discharged concentrate reject.

What is claimed is: 
     
       1. A method of operating an electrochemical separation device comprising a dilution compartment, a concentration compartment, an ion exchange membrane positioned between the dilution compartment and the concentration compartment, first and second electrodes, a first feed stream fluidly connected to the dilution compartment, a second feed stream fluidly connected to the concentration compartment, and a concentration compartment recycle stream the method comprising:
 directing the first feed stream to the dilution compartment to produce a product stream; 
 directing the second feed stream to the concentration compartment to produce a reject stream; 
 recycling the reject stream to the concentration compartment; 
 measuring electric current between the first and second electrodes; 
 periodically discharging a volume of the reject stream having a first concentration of ions in a batch cycle; and 
 replacing the discharged volume of the reject stream with an essentially equivalent volume of the second feed stream having a second concentration of ions lower than the first concentration of ions, 
 the batch cycle being determined by the electric current between the first and second electrodes, the method comprising discharging the volume of the reject stream when the electric current decreases to reach a predetermined value. 
 
     
     
       2. The method of  claim 1 , further comprising periodically reversing a polarity of the first and second electrodes, and coordinating a timing of the periodic discharge of the reject stream with a timing of the periodic reversal of the polarity. 
     
     
       3. The method of  claim 2 , further comprising exchanging flow paths of the first feed stream and the second feed stream in coordination with the timing of the periodic reversal of the polarity, such that the first feed stream is directed to the concentration compartment and the second feed stream is directed to the dilution compartment. 
     
     
       4. The method of  claim 1 , further comprising blending the reject stream with the second feed stream to produce a reject and second feed blend upstream from recycling the reject stream to the concentration compartment,
 wherein recycling the reject stream to the concentration compartment comprises recycling the reject and second feed blend to the concentration compartment. 
 
     
     
       5. The method of  claim 4 , wherein periodically discharging the volume of the reject stream comprises periodically discharging a volume of the reject and second feed blend, and
 wherein replacing the discharged volume of the reject stream comprises replacing the discharged volume of the reject and second feed blend with an essentially equivalent volume of the second feed stream. 
 
     
     
       6. The method of  claim 1 , further comprising blending the reject stream with a third feed stream to produce a reject and third feed blend upstream from recycling the reject stream to the concentration compartment,
 wherein the reject stream is recycled to the concentration compartment by recycling the reject and third feed blend to the concentration compartment. 
 
     
     
       7. The method of  claim 6 , wherein the volume of the reject stream is periodically discharged by periodically discharging a volume of the reject and third feed blend, and
 wherein the discharged volume of the reject stream is replaced by replacing the discharged volume of the reject and third feed blend with an essentially equivalent volume of the second feed stream. 
 
     
     
       8. The method of  claim 1 , further comprising periodically discharging the volume of the reject stream for about 0.5 minutes to about 2.0 minutes in batch cycles of about 15 minutes to about 25 minutes. 
     
     
       9. The method of  claim 1 , wherein the batch cycle is determined by the ionic concentration of the reject stream, the method comprising periodically discharging the volume of the reject stream when the first concentration of ions reaches a concentration sufficient to form a precipitate. 
     
     
       10. The method of  claim 9 , comprising periodically discharging the volume of the reject stream when the first concentration of ions is a concentration of greater than about 12,000 ppm total dissolved solids (TDS). 
     
     
       11. The method of  claim 9 , further comprising measuring the ionic concentration of the reject stream.